In copending U.S. patent application Ser. No. 588,969 filed concurrently herewith, which copending application is owned by the assignee of the present application and is entitled "IMPROVED POWER TRANSMISSION SYSTEM, there is disclosed a new and improved worm drive system which includes an enveloping-type worm screw and a roller worm wheel. More particularly, the roller worm wheel includes two sets of rollers inclined at an angle relative to a plane which divides the worm wheel into two symmetrical halves and which is normal to the worm wheel's axis of rotation. One set of rollers is positioned on one side of the imaginary plane of symmetry, while the other set of rollers is positioned on the opposite side of the imaginary plane of symmetry in a staggered relationship relative to the first set of rollers.
In Collier U.S. Pat. No. 921,593, a technique for cutting an eveloping-type worm screw is disclosed. The technique involves forming an hourglass screw thread using a cutter which is always directed at the central longitudinal axis of a worm screw blank. Accordingly, the hourglass screw thread is specifically designed to mate with roller teeth or fixed teeth which are always directed at the central longitudinal axis of the worm screw. The technique described in the Collier patent is, therefore, not suitable for machining an hourglass screw thread adapted to mate with the angularly positioned rollers of the roller worm wheel disclosed in the copending patent application identified above.